1. Field of the Invention
This invention pertains to the recovery of polymeric antioxidants. More particularly, it pertains to a method for isolating in essentially pure form solid polymeric antioxidants having minimal amounts of low molecular weight contaminants from a liquid phase polymerization reaction mixture.
2. Discussion of Prior Art
Recently, it has been shown by U.S. Pat. No. 3,930,047 of Dale et al and by South African Pat. No. 74/3548 of Zaffaroni that certain polymeric antioxidants offer special advantages in edibles. These references taught that questions of systemic toxicity can be eliminated if antioxidants maintain a molecular size which is larger than can be passed through the walls of the gastrointestinal tract. These references as well as other references disclosed the formation of large antioxidants by the polymerization and copolymerization of small antioxidant species. With any known polymerization technique, some monomers, dimers and trimers and other low (500 Daltons or less) molecular weight species will be present in the reaction product. These materials must be minimized if desired low gastrointestinal absorption is to be obtained. Also, in a food grade product it is desirable to minimize product contamination by solvents and reaction media.
One conventional way to minimize monomers and other low molecular weight species is to carry out the reaction under conditions which lead to very high average molecular weights for the polymer products. This offers the disadvantage of yielding a product which is not acceptably soluble in many edible oils. Another way to obtain a suitable product is to fractionally precipitate the high molecular weight material from an organic nonsolvent.
In using this precipitation method to isolate large batches of diolefin-phenolic copolymeric antioxidants, several problems were found. First, the precipitation had to be carried out under very dilute conditions with organic solvents and diluents to achieve the desired fractionation. This led to low yields of the desired antioxidant product. This required expensively large equipment for the precipitation itself and for liquid recovery as well as large liquid use rates even with efficient operation. Second, the precipitate product was a sticky wet cake which could be dried only with difficulty. Residual liquid levels were higher than desirable for a food grade product except under the most rigorous laboratory-type processing conditions. Clearly, a method of recovery which would minimize the expense and wastefulness of these separate precipitation and drying steps would be a useful improvement in the preparation of diolefin-phenolic polymeric antioxidants.